In recent years, image display devices such as portable terminals that display images are increasingly seen that have the function of automatically altering the orientation of a displayed image to facilitate viewing.
According to this function, an acceleration sensor is provided in the image display device, and when gravity acceleration is detected in this acceleration sensor, the orientation in which the image display device is being supported is estimated and the orientation of the displayed image then altered based on the estimation result.
In addition, Patent Document 1 discloses technology whereby the display orientation of an image is switched according to the attitude (position) of the case of the portable terminal device.
In the technology disclosed in Patent Document 1, the viewing orientation by which the user of a portable terminal views the screen of the portable terminal is estimated based on attitude information indicating the attitude of the case of the portable terminal. Image display is then carried out according to the estimated viewing orientation and attitude information.